Delaying Measles-Related Vaccines: Seizure Risk?

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To get answers to their questions, the researchers studied vaccination records of over 323,000 U.S. children from 2004 to 2008.

The timing of vaccinations during the first year of life didn't affect seizure rates. But delaying a measles-mumps-rubella immunization until 16 to 23 months boosted the risk of seizure from about 1 in 4,000 doses to 1 in 2,000 doses, Hambidge said.

For the vaccine that also wards off chicken pox, the rate grew from 1 in 2,000 doses to 1 in 1,000 doses, he said.

What's going on? It's possible, Hambidge said, that the immune systems of the older children are stronger, allowing them to develop fevers to fend off the weakened germs in the vaccines. The fevers can then lead to seizures.

Seizures in young children are common, said Dr. Geoffrey Weinberg, professor of pediatrics at University of Rochester School of Medicine and Dentistry in Rochester, N.Y.

"They occur in as many as 2 to 5 percent of children by age 5, most commonly at 16 to 18 months of age," Weinberg said. "They can be very scary and often result in medical care visits, but, for the vast majority, have no long-term effects."

Whatever the risk of seizures, Weinberg said it's important to get babies immunized on time so they'll be protected against measles, mumps, rubella and chicken pox. These potentially serious childhood diseases are very contagious.

As of May 9, 2014, 187 people in the United States have been diagnosed with measles this year, according to the Centers for Disease Control and Prevention. Dr. Anne Schuchat, director of the National Center for Immunization and Respiratory Diseases, said that's "the most measles cases reported in the first four months of the year since 1996." Most of those sickened hadn't been vaccinated.